Plant materials including grains contain a number of valuable components such as starch, protein, mixed linkage 1-4, 1-3 beta-D-glucan (beta-glucan), cellulose, pentosans, tocols, etc. These components, and products derived from these components, have many food and non-food uses. Consequently, there is a strong and continued industry interest for the processing of such plant materials.
Using barley grain as an example, the beta-glucan (usually up to 8% w/w) therein exists as a major component of the endosperm cell walls, with other minor components such as cellulose and hemi-cellulose (pentosans). The beta-glucan has many potential applications in the food (i.e. functional foods), pharmaceutical and cosmetic industries. Nutritional studies have suggested that inclusion of beta-glucan and tocols (i.e. tocopherol and tocotrienol) into the human diet will benefit human health.
The starch (up to 65%) in barley shows comparable functionality (i.e. thickening, gelling, paper making qualities, acid/enzyme resistance, etc.) to corn starch, which is currently used extensively for various applications. Therefore, barley starch can be substituted for corn starch in the preparation of many existing food and industrial products (i.e. modified food starches, cationic or amphoteric starches for paper industry, dextrin's for food and paper industry, adhesives, acid cut starches, etc.). Because of the aforementioned reasons, a strong and continued industry interest currently exists for the fractionation and utilization of barley grain.
A number of investigations at laboratory and pilot scale have been carried out on the fractionation of barley. In general, water, acidified water and/or aqueous alkali (i.e. NaOH or NaHCO3) have been used as a solvent for the slurrying of whole cracked barley, barley meal (milled whole barley) or barley flour (roller milled barley flour or pearled-barley flour). The slurry is then processed by techniques such as filtration, centrifugation and ethanol precipitation to separate the slurry into various components. This conventional process for barley fractionation has a number of technical problems and whilst realizing limited commercial feasibility has been limited by the expense of the product particularly for food applications.
In particular, technical problems arise because the beta-glucan in barley flour is an excellent water-binding agent (a hydrocolloid) and as such, upon addition of water (neutral, alkali or acidic environment), the beta-glucan hydrates and tremendously thickens (increases the viscosity) the slurry. This thickening imposes many technical problems in the further processing of the slurry into pure barley components (i.e. starch, protein, fiber, etc.), including clogging of the filter during filtration and inefficient separation of flour components during centrifugation.
Usually, these technical problems are minimized, if not eliminated, by the addition of a substantial quantity of water to the thick/viscous slurry in order to dilute and bring the viscosity down to a level where further processing can be carried out. However, the use of high volumes of water leads to several further problems including increased effluent water volumes and the resulting increased disposal costs. In addition, the beta-glucan, which solubilizes and separates with the supernatant (water) during centrifugation, is usually recovered by precipitation with ethanol. This is done by the addition of an equal volume of absolute ethanol into the supernatant. After the separation of precipitated beta-glucan, the ethanol is preferably recovered for recycling. However, recovery requires distillation, which is also a costly operation from an energy usage perspective.
Accordingly, there has been a need for an efficient process for the fractionation of grains which overcomes the particular problems of slurry viscosity and water usage. Moreover, there has been a need for a process which provides a high purity beta-glucan product with decreased starch and protein content.
More specifically, there has been a need for a grain fractionation process wherein a grain or grain flour is slurried in a solvent wherein beta-glucan is recovered without solubilization and wherein the solvent used for slurrying the grain or grain flour may be efficiently recycled.
A review of the prior art reveals that such a process has not been heretobefore realized. For example, there are numerous previous patents which describe various methods of fractionating grain through the above mentioned solubilization and subsequent ethanol precipitation methodology. Examples of such patents include U.S. Pat. No. 4,018,936 (Garbutt et al.), U.S. Pat. No. 5,512,287 (Wang et al.) U.S. Pat. No. 5,614,242, U.S. Pat. No. 5,725,901 (Fox), U.S. Pat. No. 6,197,952 (Fox), U.S. Pat. No. 6,113,908 (Paton et al), U.S. Pat. No. 5,169,660 (Collins), U.S. Pat. No. 5,312,636 (Myllymiaki), U.S. Pat. No. 5,518,710 (Bhatty), and U.S. Pat. No. 5,846,590 (Malkki).
Other patents also teach the use of amylase enzymes for hydrolysing starch during grain processing including U.S. Pat. No. 4,804,545 (Goering), U.S. Pat. No. 5,013,561 (Goering et al.), U.S. Pat. No. 5,082,673 (Inglett) and U.S. Pat. No. 3,912,590 (Slott).
Other patents are directed to mechanically concentrating beta-glucans by size reduction and sieving/air classification practices and include U.S. Pat. No. 5,063,078 (Foehse), U.S. Pat. No. 5,725,901 (Fox), and U.S. Pat. No. 6,083,547 (Katta).
Other patents are directed to the use of low concentration ethanol solutions in recovering beta-glucan and include U.S. Pat. Nos. 5,106,640 and 5,183,677 (Lehtomaki).
Still other patents are directed to miscellaneous grain fractionation techniques such as U.S. Pat. No. 5,106,634 (Thacker) U.S. Pat. Nos. 4,211,801 and 4,154,728 (Oughton) U.S. Pat. No. 3,950,543 (Buffa) U.S. Pat. No. 4,431,674 (Fulger) U.S. Pat. No. 5,312,739 (Shaw).